#include<stdlib.h>
#include<stdio.h>
#include<signal.h>
#include<unistd.h>

extern void err_sys(const char *, ...);
static void sig_quit(int);

int main(void)
{
	sigset_t newmask, oldmask, pendmask;

	if(signal(SIGQUIT, sig_quit) == SIG_ERR)
		err_sys("signal(SIGQUIT) error");

	sigemptyset(&newmask);
	sigaddset(&newmask, SIGQUIT);
	if(sigprocmask(SIG_BLOCK, &newmask, &oldmask) < 0)
		err_sys("SIG_BLOCK error");

	sleep(5);

	if(sigpending(&pendmask) < 0)
		err_sys("sigpending error");
	if(sigismember(&pendmask, SIGQUIT))
		printf("\nSIGQUIT pending\n");

	if(sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)
		err_sys("SIG_SETMASK error");
	printf("SIGQUIT unblocked\n");

	sleep(5);
	exit(0);
}

static void sig_quit(int signo)
{
	printf("caught SIGQUIT\n");
	if(signal(SIGQUIT, SIG_DFL) == SIG_ERR)
		err_sys("can't reset SIGQUIT");
}

